Lightweight materials for automobile construction draw considerable interest for improving fuel economy while maintaining vehicle acceleration peformance and size utility. A rapid, low-cost, reliable joining or assembly process is required to make aluminum an acceptable material of construction. Spot welding remains one of the more attractive assembly joining methods because it is simple in principle; it does not require operator skill and is a process currently in worldwide use by automobile manufacturers. Two areas of concern surrounding aluminum spot welding are electrode life and inconsistent weld quality. Many investigators have addressed these areas of concern and have offered remedies for one or the other, but the clear solution to both problems has not been advanced.
Aluminum has two attributes which cause it to perform differently than steel in resistance spot welding. First, it is a good conductor, both electrically and thermally, having about one-third the bulk resistivity of steel. Second, it develops a protective oxide coating which acts as a high resistance (or in some cases, as an insulator) on the surface of the aluminum. Little can be done to change the bulk resistivity of aluminum and still maintain desirable mechanical properties.